The present invention relates, in general, to electronics, and more particularly, to methods of forming semiconductor devices and structure.
In the past, the semiconductor industry utilized various methods and structures to form timing generators that were used to generate a timing interval for use in circuits. One common type of timing generator is illustrated in FIG. 1. For this timing generator a current source provided a current to a capacitor. An operational amplifier, configured as a comparator, compared the voltage on the capacitor to a reference voltage and generated a control signal on the output of the comparator. When the voltage on the capacitor reached the value of the reference voltage, the output of the comparator was expected to change. However, the comparator had an internal delay that caused the output to change some time after the capacitor voltage reached the reference value. This delay affected the time period generated by the timing generator. The graph to the right of the circuit illustrates the inaccuracy of the timing generator. Plot A represents the voltage on the capacitor and a plot B represents the output signal from the comparator. When the voltage on the capacitor reached the reference value at time D, the output signal from the comparator did not change state but changed at a time E that was some time period C after the capacitor voltage reached Vref. This parasitic delay of the comparator resulted in an inaccurate time period. Additionally, the delay time, time C, was also dependent on temperature and could vary also from one timing generator to another due to semiconductor process variations.
Accordingly, it is desirable to have a timing generator that more accurately forms a desired time interval, that generates a time interval that is less temperature dependent, and that generates a time interval that is less dependent on semiconductor process variations.
For simplicity and clarity of the illustration, elements in the figures are not necessarily to scale, and the same reference numbers in different figures denote the same elements. Additionally, descriptions and details of well-known steps and elements are omitted for simplicity of the description. As used herein current carrying electrode means an element of a device that carries current through the device such as a source or a drain of an MOS transistor or an emitter or a collector of a bipolar transistor or a cathode or anode of a diode, and a control electrode means an element of the device that controls current through the device such as a gate of an MOS transistor or a base of a bipolar transistor. Although the devices are explained herein as certain N-channel or P-Channel devices, a person of ordinary skill in the art will appreciate that complementary devices are also possible in accordance with the present invention. It will be appreciated by those skilled in the art that the words during, while, and when as used herein are not exact terms that mean an action takes place instantly upon an initiating action but that there may be some small but reasonable delay, such as a propagation delay, between the reaction that is initiated by the initial action.